Exploring Great Plains Nocturnal Low-Level Jet Heterogeneity and Connections to Convection Initiation

The Great Plains region of the United States often experiences a nighttime precipitation maximum during the summer months, with some of the maximum being contributed to by convection that initiates overnight. Current understanding of the processes leading to nocturnal convection initiation is limited, but it is believed the nocturnal low-level jet may be playing an important role. This study evaluates the importance of heterogeneity in nocturnal low-level jet structure to overnight convection initiation which occurs away from well-understood drivers like fronts and outflow boundaries. Observations from six nights of the 2015 Plains Elevated Convection At Night (PECAN) field campaign were used in this study establish frequency of heterogeneity in nocturnal low-level jets and draw possible connections between a heterogeneous jet and an episode of nocturnal convection initiation. Each considered case showed clear diagonal striation signatures in time-height profile observations of the boundary layer wind, which previous work has indicated as a local manifestation of spatially heterogeneous nocturnal low-level jets. This result suggests heterogenous nocturnal low-level jet structure is more common than current climatology indicates. The role of heterogeneity in triggering or supporting an episode of convection initiation on 11 July 2019 is also investigated using PECAN observations and numerical simulation tools. Initial results based on observations suggest that heterogeneity in the nocturnal low-level jet structure could lead to localized regions conducive to convergence and associated vertical motions. Numerical analysis will explore the role of the nocturnal low-level jet in transport and modification of the local environment and on the more detailed role heterogeneity could have played in ascent mechanisms. This study demonstrates the need to consider heterogeneity in the nocturnal low-level jet when forecasting for nocturnal convection initiation, especially if more strongly forced drivers are absent.